FOR 17 MONTHS NORTHERN IRELAND ENJOYED A CEASE-FIRE. NOW THE I.R.A. HAS VERY DRAMATICALLY BLOWN IT UP

AT 7:01 LAST FRIDAY EVENING, 16-year-old Neil Parker was strolling in East London with his girlfriend when a powerful blast of wind nearly knocked him to his knees. Nearly a mile away, a half-ton bomb had exploded just across from Canary Wharf, home of Europe's tallest office building. As blood-flecked pedestrians stumbled across acres of shattered glass and sirens pierced the smoke, Parker tried to calm his girlfriend, Samantha Herbert. "I thought immediately it was something to do with the I.R.A.," he said.

He was right. Less than two hours earlier, the Dublin newsroom of Ireland's main broadcast network had received...